
public class recurtionDemmmmo1 {

	static int sum(int n){
		if(n <= 1) return 1;
		if(n%2 == 0) return n + sum(n-2);
		
		return (n-1) + sum(n-2);
		
	}

	public static void main(String[] args) {

System.out.println(sum(2)-1);
	}

}
